Increase in salmon after dam removal: academic

The removal of a check dam from the Shei-pa National Park in 2011 has led to a dramatic increase in the population of the critically endangered Formosan landlocked salmon, a professor said yesterday.

The number of salmon has grown from fewer than 500 in 2001 to 5,400 this year, said National Chung Hsing University professor Lin Hsing-juh (林幸助), who started a 10-year project in 2004 with 20 other academics to monitor and research the fish.

The 15m by 3m Check Dam No. 1 of the Chichiawan Creek, one of 10 built on the river to reduce channel erosion and prevent sediment from filling a downstream reservoir, was torn down in May 2011.

The research team found that the dam left the fish vulnerable to big storms. When the creek was hit by a typhoon or flooding, the salmon would be flushed from their natural habitat in the creek’s upper reaches to points downstream, Lin said.

The cold-water fish would try to migrate upstream, but were prevented by the dam, leaving them to die in the warmer water of the creek’s lower reaches, Lin said.

During each major storm, one-third of the Formosan landlocked salmon in the region perished, he said.

The current salmon population has nearly reached the creek’s maximum capacity of 5,800 salmon, Lin said, but he added that the species is threatened by pollution caused by the production of high-mountain vegetables, fruit and tea grown nearby on Wuling Farm (武陵農場).

Nitrates in the fertilizers found in washed off soil pollute the creek and prevent the salmon from breathing, he said.

The species, a holdover from the last Ice Age, needs unpolluted waters to survive and is now found only in the country’s Cijiawan Creek (七家灣溪) and Gaoshan Creek (高山溪) in the upper reaches of the Dajia River (大甲溪).